"Boundary residues" between the folded RNA recognition motif and disordered RGG domains are critical for FUS-RNA binding

Biomolecular condensates-Prerequisites for anhydrobiosis?

It is often underappreciated that despite water being a requirement for life on Earth, organisms belonging to all taxonomic kingdoms have developed mechanisms to survive desiccation. These organisms, referred to as anhydrobiotes, accumulate specific biomolecules during or before drying that facilitate the survival of desiccation stress. Compounds utilized by a wide variety of anhydrobiotes during desiccation include metabolites such as sugars and amino acids, as well as proteins with extensive intrinsically disordered regions. Intrinsically disordered proteins that are constitutively expressed or upregulated during the onset or in preparation for desiccation include late embryogenesis abundant proteins, tardigrade disordered proteins, hydrophilins, some small heat shock proteins, and prion-like proteins. Some of these proteins form biomolecular condensates in the cellular environment. We hypothesize that phase transitions driven by anhydrobiosis-related intrinsically disordered proteins play a substantial role in enabling anhydrobiosis by (1) contributing to the downregulation of metabolic and developmental processes, (2) selectively sequestering desiccation-sensitive molecules into a "protective compartment" during drying, (3) interfering with programmed cell death signaling pathways to confer optimal time for the cell to repair after rehydration, (4) resisting intracellular volume changes to aid in membrane stabilization during desiccation, and (5) changing the biophysical properties of water to reduce desiccation-induced cellular damage. Biochemical strategies in anhydrobiotes are certainly multifaceted and may differ among systems. Nevertheless, a better understanding of the relevance of phase transitions in anhydrobiosis may allow us to get one step closer to unraveling the enigmatic phenomenon of life without water.

The ribonucleoprotein hnRNPA1 mediates binding to RNA and DNA telomeric G-quadruplexes through an RGG-rich region

hnRNPA1, a protein from the heterogeneous-nuclear ribonucleoprotein family, mediates cellular processes such as RNA metabolism and DNA telomere maintenance. Besides the folded RNA recognition motifs, hnRNPA1 has a ∼135 amino-acids long low-complexity domain (LCD) consisting of an RGG-rich region and a prion-like domain (PrLD). Biochemical data suggest that the RGG-rich region modulates the recognition of G-quadruplexes (GQs) in the telomeric repeats. Here, we utilize an in-house developed replica exchange technique (REHT) to generate the heterogeneous conformational ensemble of hnRNPA1-RGG and explore its functional significance in telomere maintenance. Single chain statistics and abundance of structural motifs, as well as consistency with experimentally reported structural data suggest faithful recapitulation of local interactions. We also introduce a protocol to generate functionally significant IDP-nucleic acid complex structures that corroborate well with the experimental knowledge of their binding. We find that RGG-box preferentially binds to the grooves and loops of GQs providing specificity towards certain GQ structures with its sequence and secondary structures. Turn-like structures expose Phe and promote stacking with the G-tetrads, while Tyr and Asn residues form essential hydrogen bonds and electrostatic interactions. Several of these residues were also identified as important by the earlier reported HSQC chemical shift data. Our binding and simulation studies also reveal that a minor population of the RGG-box can perturb telomeric GQs structure, which likely expedites the unfolding activities of hnRNPA1-UP1 at the telomeric end.

Conformational switches in human RNA binding proteins involved in neurodegeneration

Conformational switching in RNA binding proteins (RBPs) is crucial for regulation of RNA processing and transport. Dysregulation or mutations in RBPs and broad RNA processing abnormalities are related to many human diseases including neurodegenerative disorders. Here, we review the role of protein-RNA conformational switches in RBP-RNA complexes. RBP-RNA complexes exhibit wide range of conformational switching depending on the RNA molecule and its ability to induce conformational changes in its partner RBP. We categorize the conformational switches into three groups: rigid body, semi-flexible and full flexible. We also investigate conformational switches in large cellular assemblies including ribosome, spliceosome and RISC complexes. In addition, the role of intrinsic disorder in RBP-RNA conformational switches is discussed. We have also discussed the effect of different disease-causing mutations on conformational switching of proteins associated with neurodegenerative diseases. We believe that this study will enhance our understanding on the role of protein-RNA conformational switches. Furthermore, the availability of a large number of atomic structures of RBP-RNA complexes in near future would facilitate to create a complete repertoire of human RBP-RNA conformational switches.

RNA-binding proteins in breast cancer: Biological implications and therapeutic opportunities

RNA-binding proteins (RBPs) refer to a class of proteins that participate in alternative splicing, RNA stability, polyadenylation, localization and translation of RNAs, thus regulating gene expression in post-transcriptional manner. Dysregulation of RNA-RBP interaction contributes to various diseases, including cancer. In breast cancer, disorders in RBP expression and function influence the biological characteristics of tumor cells. Targeting RBPs has fostered the development of innovative therapies for breast cancer. However, the RBP-related mechanisms in breast cancer are not completely clear. In this review, we summarize the regulatory mechanisms of RBPs and their signaling crosstalk in breast cancer. Specifically, we emphasize the potential of certain RBPs as prognostic factors due to their effects on proliferation, invasion, apoptosis, and therapy resistance of breast cancer cells. Most importantly, we present a comprehensive overview of the latest RBP-related therapeutic strategies and novel therapeutic targets that have proven to be useful in the treatment of breast cancer.